utility for generating icon themes and libXcursor cursor themes

- A set of multi-layer images, one for each size
- Am XML theme description file

Each image contains all the cursors arranged in a grid; For cursors the
layers are:

- A layer with a dot for the hotspot of each cursor
- The main image or first animation frame for multi-frame animated
cursors
- The second animation frame for multi-frame animated cursors
- ...

For icons, the layers are:

- A layer with the images
- An optional layer with attachment points for emblems
- An optional layer with boxes for embedding text into icons

In practice, since loading of multilayer images is not supported by
standard image libraries, each layer is input as a separate image file.

The theme description file contains, among other things, information
about the source images to read, the location of each named cursor or
icon within the grid, and a set of aliases from names to other names.